INSIDE A NODE: The MARS project is a test of a NEPTUNE power and communications node at full power. Two specially built converters [top gray tubes] turn the 10 kilovolts on the cable [gray] into 400 volts [blue] for distribution to other nodes and scientific instruments. Only one converter operates at a time; the other acts as a backup. Within the other pressure tube are routers for the data on the cable's optical fibers. All the equipment is housed in a trawler-proof shell [orange].